1. Field of the Invention
This invention relates to methods and apparatus for thread mill drilling wherein a single tool is manipulated to first drill a hole in a workpiece and thereafter moved orbitally in the hole to form threads in the wall of the hole and then retracted from the hole.
2. Description of the Prior Art
The common approach to providing a threaded hole in a workpiece is to first drill the hole using a drill bit or the like and after removing the bit from the hole, using a tap, to tap the hole to provide threads in the wall thereof. In lieu of a tap, a thread milling tool may be used. Thread milling has only been satisfactory in larger diameter holes such as 5/8 or 3/4, and has been too slow for smaller holes. U.S. Pat. No. 2,813,280 shows a combination drill and tap, but I am not aware that this has met with commercial success.
Substantial savings in processing costs could be effected if, instead of requiring the use of separate drilling and tapping or milling tools, the same tool could be used for the entire operation because such would avoid the necessity of indexing the workpiece from one forming operation to another, or using a machine tool having separate heads for moving the drilling and tapping or milling tools successively into work performing positions. U.S. Pat. No. 3,334,366 shows a machine tool having a spindle intended to hold either a drill or a tap, but the drill must be removed before the tap may be mounted in the spindle.